An object oriented system for damage tolerance design of stiffened panels

This paper describes an interactive, integrated system for damage tolerance design of aircraft stiffened panels. The tasks supported by the system range from the initial definition of the stiffened panel configuration to the elaboration of the residual strength and crack growth diagrams, including the mesh design and the incremental crack extension analysis. The structural configuration is represented in an object oriented fashion, using a high level of abstraction and in terms of object components well-known to the designer, such as stiffeners, cracks and boundaries. Input data is performed interactively, through a user-friendly windows-based interface and the boundary element meshes are automatically designed using a rule-based strategy. Crack propagation analysis is performed with the dual boundary element method which allows for the solution of problems involving single or multiple cracks under mixed mode conditions.     

Simplification in the simulation of manufacturing systems

Given the widespread acceptance of the importance of simplicity in management science models, the scarcity of research into simplification is perhaps surprising. In the simulation of manufacturing systems, simplification is often not attempted and, on the (misguided) assumption that more detailed models are necessarily more accurate and therefore better, common practice is to build and use the most complex model that can be built in the time available. However, for cases where the only results required are averages, such as long term throughput rates, it will often be possible to reduce the model to such a simple version that an analytical solution becomes feasible and the simulation redundant. An eight stage procedure is proposed for doing the reductions and two manufacturing case studies are described.     

Proposal of a concept of future oriented machine tools for advanced manufacturing systems

In order to satisfy the recent various consumers’?needs, an advanced manufacturing system will be required. So, the innovative concept of Future Oriented Machine Tools (FOMT), which consists of four function blocks to realize the advanced manufacturing system, is proposed. The four function blocks are Management, Prediction, Observation and Strategy, and intelligent manufacturing processes are realized by utilizing these function blocks. FOMT can make a significant contribution in four stages: design stage, production scheduling stage, machining stage and post-machining stage. In the design stage, the product information such as accuracy can be evaluated in CAD, considering the manufacturing ability concurrently. In the production scheduling stage, the product schedules can be generated automatically and flexibly for the various products. In the machining stage, cutting conditions adjusted autonomously according to the machining status and machining problems. In the post-machining stage, the machining know-how data are accumulated and stored for future production and human engineers. The feasibility of it, especially the machining stage, is discussed using the developed cutting process simulator called VMSim (virtual machining simulator) from the view points of cutting force, machining error and environmental burden (CO₂ emission).     

Continuum based modeling of silicon integrated circuit processing: An object oriented approach

Continuum based integrated circuit process modeling is the dominant tool used to investigate and understand integrated circuit (IC) development. This paper describes the commonly used models for implantation, diffusion, and material growth. In addition, the supporting numerical techniques are described. This paper focuses on the implementation in object oriented code, Florida Object Oriented Process Simulator (FLOOPS). The software architecture is described for implementing models and numerics. A number of process examples are introduced and discussed.     

Object-oriented simulation to support research in manufacturing systems

Simulation is a popular tool for modelling and analysing modern manufacturing systems. Choosing an appropriate simulation approach for a long-term research activity is not an easy task. This report discusses the issues involved in selecting a simulation approach to support research in real-time resource allocation decisions in manufacturing. A review of current directions in simulation software is presented. Specialized simulation needs of university-based research are described. After evaluating our needs with respect to the available options, we found that an object-oriented programming paradigm suits our needs best.     

Using evolutionary algorithms and simulation for the optimization of manufacturing systems

This paper is concerned with an optimization method for manufacturing systems. This method can be applied to optimize problems with any type of variables (variables from a real set, e.g., conveyor speed; an integer set, e.g., size of buffer; or any general set, e.g., dispatching rules). It is based on the association of an evolutionary algorithm and a simulation model. Extensions of Michalewicz's evolutionary operators and algorithm are proposed to tackle manufacturing system problems. The particular case of stochastic models is discussed. This method is applied to an example: the configuration of a workshop producing plastic yoghurt pots. The criterion to optimize is the cost of the workshop and the three variables are the size of a silo, the size of a warehouse and a choice between two manufacturing methods. The application has been realized by connecting an evolutionary algorithm programmed in C and a simulation language.     

Tool management in flexible manufacturing systems with network part program

Recent technological developments have allowed a new concept of a part program to execute the machining operations that remove the software constraints introduced by the numerical control of machining centres. This change allows machines executing a part program to be structured as a net of operations and not linearly as normally happens in shop floors. The main advantage of using the network part program in numerically controlled machines is that it gives the system more flexibility by increasing the number of alternatives that machines can follow during work. In such a way, machines select their path in the network part program taking into account the dynamic state of resources (e.g. spindles, tools, carriers, pallets, etc.). The paper contains a study on the flexibility related to network part program exploitation in numerically controlled machines. Easy-to-calculate indicators are also defined. They estimate the potential flexibility of a network part program related to a particular product. The study has allowed the definition of a new tool management rule to be used in a flexible manufacturing system where the tools are shared dynamically among machines. The numerical results carried out on two different real cases demonstrate the validity of the new concept by quantifying the advantages in terms of throughput increment and machine idle-time reduction.     

Analysing the effects of Lean manufacturing using a value stream mapping-based simulation generator

Value stream mapping (VSM) has become a popular implementation method for Lean manufacturing in recent years. However, its limitations such as being time-consuming, its inability to detail dynamic behaviour of production processes and to encompass their complexity, have spurred us to turn to simulation. This paper introduces two new elements to the value stream mapping method. First, it describes how the value stream mapping paradigm (VSMP) can be adapted for use in simulation, introducing specially designed VSM objects. Secondly, based on the VSMP and these objects, it presents a formal modelling method and its related database structure, that drives a generator which automatically yields a simulation model of the value stream map. In this way, a model generator, using the set of objects and the model database, can generate simulation models of Current and Future VSM scenarios quickly and automatically. Additionally, algorithms for converting raw ERP data and information from a VSM drawing into tables of the structured database are developed. Finally, the formal modelling method is applied to a real company case. A Current State model of the manufacturing system and three scenarios of Future States are generated to see the effects of Lean when transforming part of the system from push to pull.     

An integrated approach to multi-criteria design and control of manufacturing systems using simulation and goal-regression

In this paper we discuss the issue of multi-criteria design and control of manufacturing systems. We also trace the development of domain-independent non-linear planners from the field of artificial intelligence. These planners automate the task of generating a sequence of actions to achieve a specified goal. The problem of conjunctive goal planning is addressed, and a parallel drawn with the design and control of manufacturing systems where multiple criteria are to be satisfied. The inability of existing approaches to facilitate optimization across multiple performance criteria is also highlighted. Finally, to ameliorate the problem an integrated approach based on goal-regression and simulation is proposed. To facilitate conflict-resolution across multiple goals, a new algorithm is developed. The approach is tested on different configurations of test systems and found to perform satisfactorily for manufacturing systems with fairly large sets of defining variables.     

Modelling and simulation of automated manufacturing systems for evaluation of complex schedules

Automated manufacturing systems have been studied widely in terms of scheduling. As technology evolves, the behaviour of tools in automated manufacturing systems has become complicated. Therefore, mathematical approaches to the analysis of complex schedules no longer reflect reality. In this paper, we propose a systematic way of conducting simulation experiments to evaluate the complex operating schedules of automated manufacturing systems. A simulation model is based on a timed Petri net to take advantage of its mathematical strength. Since a Petri net cannot itself have token firing rules, we introduce additional states called operational states. Operational states are not directly related to a Petri net, and are only used for decision making. In addition, a decision function that is responsible for the conflict resolution of a Petri net model and an operational state transition function are introduced. The parallel simulation concept is also suggested by dividing a Petri net into several independent decision sub-nets. A multi-cluster tool system for semiconductor manufacturing is analysed as an application.     

An object oriented implementation of a front tracking finite element method for directional solidification processes

This paper focuses on the numerical simulation of phase‐change processes using a moving finite element technique. In particular, directional solidification and melting processes for pure materials and binary alloys are studied. The melt is modelled as a Boussinesq fluid and the transient Navier–Stokes equations are solved simultaneously with the transient heat and mass transport equations as well as the Stefan condition. The various streamline‐upwind/Petrov–Galerkin‐based FEM simulators developed for the heat, flow and mass transport subproblems are reviewed. The use of classes, virtual functions and smart pointers to represent and link the particular simulators in order to model a phase change process is discussed. The freezing front is modelled using a spline interpolation, while the mesh motion is defined from the freezing front motion using a transfinite mapping technique. Various two‐ and three‐dimensional numerical tests are analysed and discussed to demonstrate the efficiency of the proposed techniques. Copyright © 1999 John Wiley & Sons, Ltd.     

Ceramic green tape extrusion for laminated object manufacturing

Al₂O₃ and SiC green tapes with 0.2 mm thickness used for LOM (laminated object manufacturing) were prepared from a 75 wt.% ceramic suspension in a LDPE based organic vehicle followed by extrusion. Rheological characterization of the alumina and SiC suspensions were studied. TG-DTA analysis was carried out in air and microstructures were examined by SEM.     

An optimization model for selective inspection in serial manufacturing systems

This paper describes an optimization model for allocating inspection efforts at each stage in a serial multi-stage assembly line. The model explicitly considers the economic tradeoff between product yield and inspection accuracy. The paper also shows that the use of a heuristic solution method, simulated annealing, is effective and efficient for solving the inspection allocation model. Problem instances have been developed using real production and visual inspection data provided by a local high-volume electronics manufacturer. In addition, randomly generated problems are used to evaluate the performance of the proposed heuristic.     

A genetic algorithms-based approach for design of manufacturing systems: An industrial application

This paper presents a design methodology and a genetic algorithm-based approach for redesign of a manufacturing system for a small steel pre-fabricated building manufacturer. Through the application of celular manufacturing principles, we discuss the application of the design methodology that takes a topdown approach to determine system needs and a bottom-up integrated design approach to develop the configurations of the manufacturing system. The integrated design approach uses a genetic algorithm and an AutoCAD interface to minimize the inter and intra cell material movements during cell formation. A selected set of solutions obtained are further analysed using discrete event modelling and simulation. The final results presented indicate a substantial improvement in overall performance compared to the original layout. The company has implemented a modified version of the final solution and has achieved the significant improvements in material handling and overall productivity.     

An efficient real-time deadlock-free control algorithm for automated manufacturing systems

In recent years, deadlock issue has received considerable attention in the real-time control realm of automated manufacturing system (AMS). In this paper, we propose a simple and easily adaptable deadlock avoidance algorithm using a graph theoretic approach. Unlike Petri-net based methods which are complex and static from the viewpoint that once they are constructed and implemented, it is not easy to modify them as the system configuration is changed, and operate them coupled with other shop-floor control modules such as a dispatching controller, our algorithm can be used cooperatively with a dispatching controller and expanded with little modification. The core of the algorithm consists of two modules: resource allocation policy and a cycle detection method. In particular, the resource allocation policy is of importance in our algorithm because even though the cycle detection method is employed, deadlock may occur under wrong resource allocation policies. Throughout this paper, we propose a quasi two-step resourceallocation policy with which our deadlock avoidance algorithm can detect and avoid deadlock just one step before deadlock.     

A formal structure for discrete event simulation. Part II: Object-oriented software implementation for manufacturing systems

This paper describes the development of a prototype object-oriented software system for discrete event simulation and the embedded decision processes of a system being modeled based on previously defined formalism [1] and the Smalltalk programming language. The paper addresses the modular and structured representations of physical and logical entities of a manufacturing system for simulation modeling in the form of reusable software objects. The software takes advantage of the natural link between object-oriented programming and simulation and utilizes inheritance and other features of object-oriented programming to achieve modular yet uniform representation at every level of the model. After giving a brief overview of the object-oriented modeling environment and the relationships between software objects and formalism constructs, a small number of object classes and their operations are summarized. The intelligent entities of the formalism utilize a knowledge-based non-programmed decision mechanism implemented in Smalltalk.     

A study of scheduling rules of flexible manufacturing systems: A simulation approach

This study examines the effects of scheduling rules on the performance of flexible manufacturing systems (FMSs). Several machine and AGV scheduling rules are tested against the mean flowtime criterion. In general, scheduling rules are widely used in practice ranging from direct applications as a stand-alone scheduling scheme to indirect application as a part of complicated scheduling systems. In this paper, we compare the rules under various experimental conditions by using an FMS simulation model. Our objective is to measure sensitivity of the rules to changes in processing time distributions, various levels of breakdown rates, and types of AGV priority schemes. A comprehensive bibliography is also presented in the paper.     

Image-based adaptive crosshatch toolpath generation for laminated object manufacturing

The adaptive crosshatching concept has been introduced for better waste material removal process in Laminated Object Manufacturing. However, the existing approaches that involve a STereoLithography model require additional information from other sources for determining adaptive crosshatch patterns, and for determining the toolpath from intersection points between these customised patterns and cross-sectional contours on their associated layers. Visual representation, on the other hand, seems to be more logical in practice for generating an adaptive crosshatch toolpath. Therefore, the image processing technique has been applied in this research for ease of adaptive crosshatch toolpath generation. For this approach, a uniform crosshatch pattern is created first as a common platform for the entire model. The pattern is modified next for each layer before being mapped onto the layer to determine the toolpath. An algorithm has been developed, and successfully implemented in the LabVIEW program. Some examples are illustrated in this paper to demonstrate the proposed approach.     

An effective part-selection model for production planning of flexible manufacturing systems

This paper presents an integer programming model for existing FMS users to select the most cost effective set of parts to run simultaneously on an FMS during a specified production horizon. Two heuristic solution algorithms are developed by dividing the part-selection procedure in two stages. One stage deals strictly with the limitations on machining time, storage capacity, and AGV time. For the other stage, three different stages are used to choose a set of pan solely based on tooling and fixture constraints. The best algorithm-strategy combination has been identified and proved to be very efficient in finding optimal or near optimal solutions.     

Modelling for agile manufacturing systems

To address the challenges of a rapidly changing manufacturing market, a new type of manufacturing system with characteristics of reconfigurability, reusability and scalability, an agile manufacturing system (AMS) has to be developed. Reconfigurability is an essential feature of AMS. Such a system can use basic building blocks, both hardware and software, which can be reconfigured quickly and reliably. A fundamental early step in the reconfiguring process for an agile manufacturing system is to develop a model that adequately describes the proposed system, in order to be able to study and evaluate the impact of the reconfiguring decision on the system performance, before its construction. Therefore, the rapid modelling and reusable modelling capabilities are demanded. In this paper, an Object & Knowledge-based Interval Timed Petri-Net (OKITPN) approach is proposed, which provides an object-oriented and modular method of modelling manufacturing activities. It includes knowledge, interval time, modular and communication attributes. The features of object-oriented modelling allow the AMS to be modelled with the properties of classes and objects, and make the concept of software IC possible for rapid modelling of complex AMSs. Once all of the Interval Timed Petri-Net (ITPN) objects are well defined the developers need to consider only the interfaces and operations relating to the ITPN objects. In order to demonstrate the capability of the proposed OKITPN, it has been used to model rapidly AMSs that are reconfigured according to requirements.